1. Field of the Invention
The present invention relates to a mobile station positioning system for positioning a mobile station (MS) connected to a code division multiple access (CDMA) mobile communication network, and more particularly, to a method for correcting positioning errors of the mobile station positioning system in the CDMA communication system, which is capable of correcting the positioning errors due to a delayed time generated when a PN code of a base station transceiver subsystem (BTS) is received in the MS via a repeater as one of information used for positioning the MS in the position determination entity (PDE).
2. Discussion of the Related Art
FIG. 1 illustrates a construction of a conventional mobile station positioning system 30.
Referring to FIG. 1, the mobile station positioning system 30 serves as an application server managed by a mobile communication manager or a contents provider of providing a positioning information service. The mobile station positioning system 30 includes a location service center (LSC) 31, a mobile station positioning center (MPC) 32, a position determination entity (PDE) 33, and a database (DB) 34.
If the LSC 31 requests a present positioning information of a specific mobile station (MS) 10 so as to provide a service based thereon, the MPC 32 receives the positioning information of the MS 10 from a mobile communication network 20 and transmits the received positioning information to the PDE 33.
At this time, the positioning information includes a pseudo random noise (PN) code of a plurality of base station transceiver subsystems (BTSs), a reception sensitivity (Ec/Io), a relative propagation delay time between the BTSs based on the PN code, a system identification code (SID), a switching identification code (NID) and a BTS identification code (BID), etc.
Further, the positioning information of the MS 10 is transmitted to the MPC 32 via a sequence of the BTS 21 belonging to a cell of the MS 10, a base station controller (BSC) 22 and a mobile switching controller (MSC) 23.
The PDE 33 receives the positioning information of the MS 10 from the MPC 32, thereby positioning the MS 10 in such a general manner of a time deference of arrival (TDOA).
The general TDOA manner is performed in the following steps.
First, the PDE 33 analyzes the positioning information of the MS 10 received from the MPC 32, using the DB 34 for storing therein position information of the plurality of BTSs belonging to the mobile communication network and the PN code information of the plurality of BTSs, etc.
Next, the PDE 33 calculates, using the triangulation method known in the art, latitude and longitude values corresponding to a cross point of nonlinear hyperbolas due to a distance difference between the MS 10 and three or more than neighboring BTSs in order to receive the present positioning information of the MS 10, thereby transmitting the calculated positioning information (that is, the latitude and longitude values) to the MPC 32.
After that, the MPC 32 transmits the received positioning information to the LSC 31 requesting the present positioning information of the MS 10. Accordingly, the LSC 31 allows a service requester to be served based on the present positioning information of the MS 10.
Meanwhile, in case the MS 10 receives the positioning information via the repeater installed in a shade area such as in a building or a subway, etc., comparing with the case of the repeater not being installed, since a relative propagation delay time difference occurs between the plurality of the BTSs based on the PN code, the conventional mobile station positioning system 30 has a drawback of generating the positioning errors when the PDE 33 performs positioning of the MS 10.
FIG. 2 illustrating a conventional state in which the MS receives the positioning information in case the repeater is not installed in the mobile communication network.
For example, referring to FIG. 2, the MS (S4) is at a distance (R0) from the BTS (a reference BTS) (S1) of the cell which the MS (S4) belongs to, being at the distance (R1) from a neighboring BTS (S2), and being at the distance (R2) from another neighboring BTS (S3). Further, the repeater is not installed between the MS (S4) and the respective BTSs (S1, S2 and S3).
Accordingly, in this case excepting a fading effect, etc., when the BTS (S1) is the reference BTS, the MS (S4) receives the positioning information delayed for a time proportional to the distance R1−R0 from the neighboring BTS (S2), and receives the positioning information delayed for a time proportional to the distance R2−R0 from another neighboring BTS (S3).
Actually, referring to FIG. 3, the PN codes received from the BTSs (S1, S2, S3) to the MS (S4) represent the reception sensitivity (Ec/Io) over a predetermined level, and more particularly, having a time at which the MS (S4) receives the PN code (PN6) of the reference BTS (S1) as a reference time, the PN code (PN12) of the BTS (S2) is delayed for a t0 time and received, and the PN code (PN100) of the BTS (S3) is delayed for a t1 time and received.
FIG. 4 illustrates a conventional state in which the MS receives the positioning information in case the repeater is installed in the mobile communication network.
In the meanwhile, referring to FIG. 4, the MS (S4) is at the distance (R0) from the BTS (the reference BTS) (S1) belonging to the cell of the MS (S4), being at the distance (R1) from a neighboring BTS (S2), and being at the distance (R2) from another neighboring BTS (S3). Further, the repeater is not installed between the MS (S4) and the respective BTSs (S1 and S2), but the repeater (RP1) is installed between the MS (S4) and the BTS (S3).
Accordingly, in this case, when the BTS (S1) is the reference BTS, the MS (S4) receives the positioning information delayed for the time proportional to the distance R1−R0 from the neighboring BTS (S2), and receives the positioning information delayed for the time proportional to the distance R2−R0 from another neighboring BTS (S3) and a delayed time due to the repeater itself (RP1).
Actually, referring to FIG. 5, the PN codes received from the BTSs (S1, S2, S3) to the MS (S4) represent the reception sensitivity (Ec/Io) over the predetermined level, and more particularly, having the time at which the MS (S4) receives the PN code (PN6) of the reference BTS (S1) as the reference time, the PN code (PN12) is delayed for the t0 time and received from the BTS (S2), but the PN code (PN100) is delayed for the t2 time and received from the BTS (S3). That is, the PN code (PN100) is longer delayed for the delayed time (t2−t1) due to the repeater (RP1) and received from the BTS (S3) to the MS (S4), comparing with the repeater (RP1) not being installed.
Therefore, even though the distance between the MS (S4) and the BTS (S3) is actually R2, in case the PDE 33 performs the positioning for the MS (S4) so as to calculate the distance between the MS (S4) and the BTS (S3), a distance error is generated as much as the distance (t2−t1)*C (C indicates a velocity of light) corresponding to the delayed time (t2−t1) due to the repeater (RP1).
The conventional mobile station positioning system has a disadvantage in which the distance error causes the positioning error to occur when the PDE 33 performs the present positioning for the MS (S4) on basis of the positioning information of the MS (S4) received from the MPC 32.